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Jun 06, 2019, 09:58 PM
Just Plane Nutts
AirDOGGe's Avatar
Quote:
Originally Posted by KiwiKrawler
The above ^^^^^ bit of documentation sort of blows this theory out of the water. So to speak. ��������

The above doc specifies centrifugal pumps.

We are dealing with axial flow pumps. Big difference.

Still afloat.
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Jun 06, 2019, 10:27 PM
Registered User
KiwiKrawler's Avatar
Quote:
Originally Posted by AirDOGGe
The above doc specifies centrifugal pumps.

We are dealing with axial flow pumps. Big difference.

Still afloat.
The theory I was relating to...was the erroneous suggestion that a pumps impeller will move entrapped air. All pumps with an impeller come under the umbrella of being centrifugal. The point being...all the different variations will not prime if they contain a air.
Jun 07, 2019, 01:57 AM
Just Plane Nutts
AirDOGGe's Avatar
Quote:
All pumps with an impeller come under the umbrella of being centrifugal.
I wholeheartedly disagree.

The centrifugal principal pump and the axial flow pump are two completely different animals with their own limitations and advantages. Only one uses centrifugal force to accelerate and pressurize the medium being pumped. There are also pumps with impellers that use displacement tech and vane pumps that use a rotor with sliding vanes.
Last edited by AirDOGGe; Jun 07, 2019 at 02:03 AM.
Jun 07, 2019, 02:19 PM
Registered User
KiwiKrawler's Avatar
Quote:
Originally Posted by AirDOGGe
I wholeheartedly disagree.

The centrifugal principal pump and the axial flow pump are two completely different animals with their own limitations and advantages. Only one uses centrifugal force to accelerate and pressurize the medium being pumped. There are also pumps with impellers that use displacement tech and vane pumps that use a rotor with sliding vanes.
You are right. And I’m not disputing those two pumps are completely different. And I never said they were THE SAME. What I said is they come under the same umbrella. Or category. Or group.

And once again. The point I was making...was about the erroneous suggestion that an impeller will move entrapped air.
Jun 08, 2019, 12:14 AM
Just Plane Nutts
AirDOGGe's Avatar
I don;'t know where they get their terminology, but I DO see that mentioned in one other site. I'll give you that.

The one that they refer to as a "radial" pump is what is normally called a centrifugal flow pump.

Quote:
Centrifugal pumps are a sub-class of dynamic asymmetric work-absorbing turbo-machinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.
Quote:
An axial-flow pump is a common type of pump that essentially consists of a propeller (an axial impeller) in a pipe.... Fluid particles, in course of their flow through the pump, do not change their radial locations since the change in radius at the entry (called 'suction') and the exit (called 'discharge') of the pump is very small. Hence the name "axial" pump.

https://en.wikipedia.org/wiki/Centrifugal_pump

https://en.wikipedia.org/wiki/Axial-flow_pump

Until today I have never heard anyone or anything refer to an axial flow pump as "centrifugal". The world is always full of surprises.


I suppose the key detail to keep in mind here is that a "centrifugal class" axial pump does not mean centrifugal or radial (center to outer edge) flow, as is the case with a "centrifugal class" centrifugal pump. It's all good.
Last edited by AirDOGGe; Jun 08, 2019 at 12:23 AM.
Jun 08, 2019, 09:59 AM
Registered User
KiwiKrawler's Avatar
Change in configuration of the boat. Will heed the advice of AirDOGGe and try the battery as far back as possible to keep the bum planted and try and stop the fast spins and loss of prime. Also dropped a 4800kv motor in to try. Will probably just make more noise than the 3000-4000kv in and out runners I’ve been trialing with no speed increase. Will shoot a video to compare....
Jun 08, 2019, 11:12 AM
Registered User
Youngsta's Avatar
Yeh there enough room for a good 3 blade prop,,
I got accused of speeding my vids up when I
used them in my 19mm jet unit,,
plenty of grunt and no need to let off the trigger,,
very tough little drives,,you could drive a car over them,,
maybe 7 years ago,,
GREEN SALMON (4 min 6 sec)
Jun 08, 2019, 12:30 PM
Just Plane Nutts
AirDOGGe's Avatar
Quote:
Originally Posted by KiwiKrawler
Change in configuration of the boat. Will heed the advice of AirDOGGe and try the battery as far back as possible to keep the bum planted and try and stop the fast spins and loss of prime. Also dropped a 4800kv motor in to try. Will probably just make more noise than the 3000-4000kv in and out runners I’ve been trialing with no speed increase. Will shoot a video to compare....

Trouble with very high KV motor is that they usually lack torque compared to an equal size/make motor with a lower KV. The higher unloaded RPMS comes from winding LESS coils of wire in the stator.

The ones I'm using are 3300KV 2850 inrunners (28mm dia x 50mmL) I had left over from my Joysway Infinity Offshores when I upgraded them to Leopard inrunners. Gobs of power. I use to see replacement Joysway motors available but everyone is sold out now. https://www.snapdeal.com/product/joy...r/630520714492

I also used the stock ESCs:
Last edited by AirDOGGe; Jun 08, 2019 at 12:40 PM.
Jun 08, 2019, 01:31 PM
Registered User
Kayaker's Avatar
Quote:
Originally Posted by Youngsta
...plenty of grunt and no need to let off the trigger.
I liked the great river action and you have excellent piloting skills. I’m glad your boat didn’t sink; it would be hard to find in that soup.
Jun 08, 2019, 07:12 PM
Registered User
KiwiKrawler's Avatar
Quote:
Originally Posted by Youngsta
Yeh there enough room for a good 3 blade prop,,
I got accused of speeding my vids up when I
used them in my 19mm jet unit,,
plenty of grunt and no need to let off the trigger,,
very tough little drives,,you could drive a car over them,,
maybe 7 years ago,,
Great vid Youngsta and indeed excellent piloting skills in that quagmire. Interested to know if the 19mm drive you were using was one of your own ones....or the nqd. And yes a good three bladed impeller takes these things to the next level.
Jun 08, 2019, 07:46 PM
Registered User
KiwiKrawler's Avatar
Quote:
Originally Posted by AirDOGGe
Trouble with very high KV motor is that they usually lack torque compared to an equal size/make motor with a lower KV. The higher unloaded RPMS comes from winding LESS coils of wire in the stator.
Yes the lack of torque of a higher kv motor is a given. But my question is how much torque does a 19mm impeller actually really need. I have already trialled both in runners and out runners of similar kv(3200ish) with pretty much identical results.
We know inherently outrunners have more torque by sheer virtue of the fact they have more rotational mass. As has been stated numerous times on multiple posts on here, the outrunners will exhibit torque rotation of the hull particularly on the initial squirt of the throttle(which obviously is advantageous in self righting boats)...but also I have found it effects the handling and turning of the boat in a negative way. The narrower the hull...the more pronounced the torque rotation.

In the 1:1 world of tuning carburettors in race cars...there’s an adage that “flow equals torque”. So bringing that theory to a scale jet drive then once you have “flow” through the drive...then you will have “torque”. In that case you only really need a ton of power on initially starting the impeller rotating...as once it’s spinning the water flow is providing torque. Once my boats on the water I very rarely...if ever unless I hit something...button off. So I feel a massive amount of “start up” torque is unnecessary.

Ding ding....round two..... 😬
Jun 08, 2019, 11:28 PM
Just Plane Nutts
AirDOGGe's Avatar
--> Jet drives can use all the torque your motor can produce, assuming the pump is not overpowered with a motor too large for it. Torque means rotational power, and it takes more power to draw up water and force it through a tapered nozzle under pressure than to spin a propeller in open water.


--> THOUGH I use inrunners in my NQD boats, I have considered dropping the surplused 2842 outrunner from my Barbwire XL in one of my Tear hulls and giving it a tryout. The motor size is ideal, and at 2800KV unloaded should not be overbearing on the drive on 3S. Under full load my inrunner is probably dropping into that same KV range anyway. The outrunner should suffer little RPM drop in relation.


--> I experienced plenty of torque AND gyroscopic precession issues when I jetted a little FT007 with the 19mm drive and powered it with a 24mm 3500KV outrunner. Being such a small boat, the symptoms were more severe.

With 3S power installed a full throttle blip at rest could roll the boat 360 degrees (torque). Also the boat would want to dive in left turns or lift the bow and spin-out turning to the right (gyroscopic precession). Running it on 2S made it controllable since the unwanted forces multiply with RPM increase. The Proboat River Jet experiences some of this rolling, with members who refitted inrunners into theirs reporting an improvement in handling.

But this is a TEAR INTO thread, and those relatively wide and near-flat bottom hulls do not suffer these rolling issues with 28mm inrunners. The problem is greatest with narrow, self-righting hulls that do not use flood chambers to flip back over. Since my FT007 experiences a few years back, I've always suggested people steer away from those for jet modding, even though their super-low price makes it tempting.




No sense in going into the carburetor analogy. Greater torque from greater flow where carbs are concerned is referring to more power generated from the engine via more air/fuel charge in the cylinders. No comparison to jet drive pump flow.



No "ding ding"s here,.... keep discussions civil please. It's all for fun.
Jun 09, 2019, 12:10 AM
Registered User
KiwiKrawler's Avatar
Quote:
Originally Posted by AirDOGGe
No "ding ding"s here,.... keep discussions civil please. It's all for fun.
Nothing but civil. Apologies if you took my sarcastic humour the wrong way. It is all for fun...and your input in our healthy conversations is welcomed and appreciated.
Jun 09, 2019, 03:45 PM
Just Plane Nutts
AirDOGGe's Avatar
No biggie.


Regarding what I said about the 11-inch FT007 hull, the one exception I made about not recommending it for a jet project was when I suggested it to wparsons.

He plans on printing a rather smallish 15mm drive and (hopefully) power it with a diminutive 2030 or 2040 inrunner. I believe the boat could handle that set-up without the overpowering or degraded handling issues I suffered with fitting that hull with the larger NQD hardware, as the rotating mass of the smaller motor's core and the tiny pump impeller would be minimal.
Jun 10, 2019, 06:37 AM
Registered User
KiwiKrawler's Avatar
OK this was my test run with the battery at the back of the boat to help plant the bum and attempt to stop the fast spins. Definitely the worst the boat has ever been with regard to handling and random loss of prime. Surprised me being honest.

Tear Into with weight towards the back (0 min 50 sec)


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